Liquid crystalline solution

Poly(/)-phenylenctcrcphthalamiclc) forms a liquid crystalline solution and can be spun into a fiber with a very high orientation these fibers have excellent tensile and thermal properties. These high-modulus fibers are suitable as reinforcing materials in technical applications. 

This polymer can be prepared from p-phenylenediamine and terephthaloyl chloride. The polymer is highly crystalline and, thus, difficult to keep in solution. Sufficiently high molecular weight polymers can be obtained by solution polymerization using a special solvent system. This ridged rod polymer can form a liquid crystalline solutions.7,9 14... 

Liquid crystalline solutions as such have not yet found any commercial uses, but highly orientated liquid crystal polymer films are used to store information. The liquid crystal melt is held between two conductive glass plates and the side chains are oriented by an electric field to produce a transparent film. The electric field is turned off and the information inscribed on to the film using a laser. The laser has the effect of heating selected areas of the film above the nematic-isotropic transition temperature. These areas thus become isotropic and scatter light when the film is viewed. Such images remain stable below the glass transition temperature of the polymer. 

Fig. 29 The observed strength as a function of the initial modulus of filaments taken from a single yarn of cellulose II spun from a liquid crystalline solution compared with the calculated curves [26]...

Liquid crystalline solution. A phase transition occurs at this point and the system shows a high degree of order. These systems inevitably have significantly different features from those above. 

Formation of band textures in HPC liquid crystalline solutions was studied by Navard (86) and Takaheshi et al. (94). Upon shearing, some polymeric liquid crystals develop a particular texture which is called "band texture" consisting of fine equidistant lines when viewed under crossed polars. In HPC-H2O mesomorphic solutions these bands are exhibited when the solution is allowed to freely relax after shearing. 

Suto et al. (102) studied the effects of salts on the turbidity and viscometric behavior of HPC mesophases in water and the rheology of liquid crystalline solutions of HPC in m-cresol (103). Suto (104) found that crosslinking HPC mesophases in water destroyed their order. 

Bheda et al. ( ) showed that cellulose triacetate forms a mesophase in dichloroacetic acid. Navard and Haudin (18) examined the thermal behavior of liquid crystalline solutions of CTA in TFA. Navard et al. (23) studied the isotropic to anisotropic transitions of solutions of cellulose triacetate in TFA using differential scanning calorimetry. Navard and Haudin (S2) studied the mesophases of cellulose and cellulose triacetate calorimetrically. Navard et al. (83) report similar studies. Meeten and Navard (97) showed the twist of the cholesteric helicoidal structure of CTA and secondary cellulose in TFA is left-handed. 

Sixou et al. (101) showed the circular dichroism of cholesteric CTA solutions in TFA depends on the CTA molecular weight. The intensity of the circular dichroic peak increases with molecular weight. Meeten and Navard (97) studied gel formation and liquid crystallinity in TFA-H2O solutions of CTA. When water was added to a liquid crystalline solution of CTA in TFA a gel phase formed presumably by the formation of crosslinks due to hydrogen bonding. They interpreted their results that liquid crystalline ordering involves both inter- and intramolecular forces. 

Bheda et al. (2Q) wet spun CTA fibers from liquid crystalline solutions in TFA. Surprisingly, they found the fibers have the CTA-I morphology. O Brien (Ifi) spim CTA fibers from TFA-CH2CI2 and TFA-H2O solutions as did Hong et al. (17) from TT A-CH2Cl2 solutions. In... 

If one follows the solution viscosity in concentrated sulfuric acid with increasing polymer concentration, then one observes first a rise, afterwards, however, an abrupt decrease (about 5 to 15%, depending on the type of polymers and the experimental conditions). This transition is identical with the transformation of an optical isotropic to an optical anisotropic liquid crystalline solution with nematic behavior. Such solutions in the state of rest are weakly clouded and become opalescent when they are stirred they show birefringence, i.e., they depolarize linear polarized light. The two phases, formed at the critical concentration, can be separated by centrifugation to an isotropic and an anisotropic phase. A high amount of anisotropic phase is desirable for the fiber properties. This can be obtained by variation of the molecular weight, the solvent, the temperature, and the polymer concentration. 

The bis(2-ethylhexyl) sodium sulfosuccinate system was initially investigated because its structure of liquid crystalline solution phases and mechanism of solubilization with water had been reported by Rogers and Winsor (10). In our studies, we substituted methanol for water. Table I lists critical micelle concentrations for bis(2-ethylhexyl) sodium sulfosuccinate, triethylammonium linoleate and tetradecyldimethylammonium linoleate in methanol and 2-octanol at 25°C. Literature references for critical micelle concentrations in methanol are sparse, and it has even been suggested that in polar solvents such as ethanol, either micellization does not occur or, if it does, only to a small degree (4). The data of Table I show that micellization occurs in methanol at low concentrations. 

In addition to the above effects, the intermolecular interaction may affect polymer dynamics through the thermodynamic force. This force makes chains align parallel with each other, and retards the chain rotational diffusion. This slowing down in the isotropic solution is referred to as the pretransition effect. The thermodynamic force also governs the unique rheological behavior of liquid-crystalline solutions as will be explained in Sect. 9. For rodlike polymer solutions, Doi [100] treated the thermodynamic force effects by adding a self-consistent mean field or a molecular field Vscf (a) to the external field potential h in Eq. (40b). Using the second virial approximation (cf. Sect. 2), he formulated Vscf(a), as follows [4] ... 

The benzobisazole family of rigid-rod polymers is soluble in acidic solvents such as PPA, methanesulfonic acid, chlorosulfonic acid, 100% sulfuric acid and Lewis acid salts such as antimony trichloride and bismuth trichloride. More recently, PBZT has been reported [22] to form liquid crystalline solutions in nitromethane containing aluminum trichloride or gallium trichloride. Since the glass transition temperature of these materials is above their decomposition temperature, they must be processed from solution. 

Other structural variations on the rigid-rod PBZXs have encompassed a variety of changes that affect the backbone geometry. Deviation from 180° para-catenation has been investigated by a number of researchers for improved processability. Solution properties are of particular interest in an effort to determine concentration effects on the ability to form liquid crystalline solutions. Most notable backbone deviations have been the ABPBT, ABPBO and ABPBI systems which are characterized by catenation angles of 162°, 150°, and 150° respectively. They are classified as extended chain systems because of the unrestricted rotation between the repeat units. The polymer backbone can... 

Many ccllulosic derivatives form anisotropic, i.e.. liquid crystalline, solutions, and cellulose acetate and triacetate are no exception. Various cellulose acetate anisotropic solutions have been made using a variety ol solvents. The nature of Ihe polymer -solvent interaction determines the concentration at which liquid crystalline behavior is initiated. The better the interaction, the lower the concentration needed to form the anisotropic, birclringenl polymer solution. Strong organic acids, eg, trifluoroac etic acid, are most effective and can produce an anisotropic phase with concentrations as low as... 

Applications. The polyamides have important applications. The very high degree of polymer orientation that is achieved when liquid crystalline solutions are extruded imparts exceptionally high strengths and moduli to polyamide libers and lilms. DuPont markets such polymers, e g. Kevlar, and Monsanto has a similar product, e.g.. X-500. which consists of polyamide and hydrazide-lype polymers. Liquid-crystal polymers arc also used in olccirnnpnc displays. 

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